1. Field of the Invention
The present invention relates to an improved cement solidification treatment of radioactive spent ion exchange resins exhausted from nuclear power plants.
2. State of the Art
As one of the means for solidification and disposition of spent ion exchange resins exhausted from, for example, a PWR type nuclear power plant, which was used for treating concentrated boric acid-containing waste water, there is used "plastics solidification". The plastics solidification achieves a higher volume reduction, but has drawbacks of the complicated process and the high treatment cost.
As a simple and less expensive solidification process, "cement solidification" has been tried. the weakness of this process is the low volume-reduction. The content of the resin particles in the solidified products is 5-10% (dry basis), and the bulk volume of the resin which can be packed in one 200-liters steel drum can ranges from only 35 to 70 liters (in terms of volume ratio, 17.5-35%) at highest. This limitation is inevitable because a cement-solidified product with a higher content of spent ion exchange resins will expand and break down when it is immersed in water.
It is considered that the expansion of the solidified product is due to expansion of the resin particles, and that the expansion of the resin particles is caused by swelling due to absorption of water and adsorption of soluble contents of the cement.
In order to improve the situation, efforts have been made to improve the properties of the solidified products. For instance, addition of caustic soda in an amount of 3-5% based on the resin, solidified products of better water-resistance can be obtained. However, the content of the resin particles in the 200-liters steel drum can may be increased to only 60-70 liters, and thus, there is no substantial improvement in the volume reduction.
From the view to eliminate the cause of swelling of the resin particles, it has been tried to coat the surface of the particles with water-resistant material such as a polyester. This was found effective, but the process will be more complicated due to the use of organic materials.